The present invention relates to bicycle power train systems and, more specifically, to debris venting power train cogs that interact with a flexible drive member to communicate rider energy between the pedals and a driven wheel.
Commonly, the front and rear tires of a bicycle are supported by respective drop out assemblies that provide the connection between a skewer, axle or hub of a wheel assembly and the frame of the bicycle. With respect to the rear wheel assembly, a flexible or endless drive, such as a belt or chain, extends between a crankset associated with the pedals, and a gear set that is drivingly associated with the rear wheel. Those skilled in the art will appreciate the structural and vernacular distinctions with respect to bicycle drive systems equipped with a belt as compared to those equipped with a chain. That is, it is appreciated that many belt driven drive system are equipped with pulleys and/or splined drive members or cogs as compared to the many toothed gears associated with chain driven systems.
As used herein, a drive member of the drive train is that portion of the bicycle drive system that is connected to, and directly driven by, the bicycle pedals. A flexible drive or flexible drive member, such as a chain and preferably a belt, is operatively associated with the drive member and communicates a drive force to a driven member. The driven member is operatively associated with a wheel assembly so that rotation of the driven member rotates the wheel assembly. Either or both of the drive and driven member may include more than one drive surface whose interaction with the flexible drive member alters the gearing of the drive train.
Regardless of the type of flexible drive associated with the drive system, the endless drive must be appropriately adjusted so as to maintain a desired operational interaction between the respective drive and driven members of the drive system and the endless drive member. Commonly, with chain and belt systems, the endless drive is adjusted or “tensioned” by adjusting the position of the rear wheel axle relative to an axis of rotation of the drive member or crankset. Operation of a screw or other adjuster, commonly referred to as a tensioner system, linearly translates the axle relative to the crankset until a desired orientation of the drive system is achieved. Efficient operation of the power train depends in large part on the efficient and secure interaction between the flexible drive member and the corresponding cogs or gears. Said in another way, during operation of a bicycle, the flexible drive member must be maintained at a generally constant position relative to each of the drive and driven members to provide efficient interaction between the rider and the drive system and/or to even maintain the operability of the bicycle.
Any debris between the flexible drive member and the drive and driven members of the power train can create a less than desired rider condition and even render the bicycle, at least temporarily, inoperable due to complete derailing of the flexible drive member from the drive system. Radial and/or lateral translation of the flexible drive member in directions away from aligned interaction with the drive and driven members is generally caused by debris disposed between the flexible drive member and the drive and drive members of the drive system Debris such as snow, mud, or rigid debris, such as stones or gravel, captured between the endless drive and the cog or gear can result in damage to the flexible drive member and/or disengagement or unexpected and undesired derailing of the flexible drive member from the rotating drive members.
Chain driven bicycle power trains are somewhat better suited than belt driven power trains to tolerate incidence of debris in the power train. The generally planar and non-overlapping shape of the gears and the omission of any open ended cavities reduces the likelihood that road or other debris will be retained in the gear or sprocket and carried in a location associated with interaction of the gear and the chain. The fairly robust metal structure common to many gears or sprocket and chain drive systems makes it more likely that any debris introduced between the chain and the gear will be most likely small so as to not interfere with operation of the power train and/or crushed or ejected during interaction of the chain and the gear. Furthermore, the generally pointy nature of the teeth of the gears and the repeated insertion and removal of the teeth from the cavities of the chain facilitates maintaining a generally clean and fully operational flexible drive system. Any dirt or debris that may accumulate in the voids of the chain is commonly ejected toward the outside of the chain as the teeth of the gears or sprockets mesh with the chain.
Unlike chain drive bicycle power train systems, many belt driven power train systems have a construction that is opposite the interaction of chain driven power train systems. That is, the belt commonly includes a number of teeth that each individually cooperates with a corresponding cavity formed on a circumferential face of a corresponding cog. Any debris between the cog and the belt becomes captured thereat and detracts from the efficient interaction between the belt and the cog. The generally planar but toothed shape of the belt prevents the venting of debris from the power train in a manner similar to that achieved with chain and sprocket power train systems. Although the belt driven power train systems are generally quieter than chain driven power train systems, such systems are less tolerant and accommodating of debris between the belt and the cog.
Accordingly, there is a need for a cog that cooperates with a belt in a drive or driven manner and which is constructed to accommodate debris so that such debris does not interfere with the efficient interaction between the cog and the belt. There is also a need for a bicycle power train assembly having one or more cogs that vents debris from the power train system in a manner that does not interfere with the operability of the adjacent cogs.